State of Polar Sea Ice – June 2013: Arctic Sea Ice Decline and Antarctic Sea Ice Gain

July 5, 2013 by weatherdem 3 Comments

Global polar sea ice area in June 2013 remained at or slightly above climatological normal conditions (1979-2008).  This follows early 2013 conditions’ improvement from September 2012′s significant negative deviation from normal conditions (from -2.5 million sq. km. to +500,000 sq. km.).  Early austral fall conditions helped create an abundance of Antarctic sea ice while colder than normal boreal spring conditions helped slow the rate of ice melt in the Arctic.

The NSIDC made a very important change to its dataset in June.  With more than 30 years’ worth of satellite-era data, they recalculated climatological normals to agree with World Meteorological Organization standards.  The new climatological era runs from 1981-2010 (see Figure 5 below).  What impacts did this have on their data?  The means and standard deviations now encompass the time period of fastest Arctic melt.  As a consequence, the 1981-2010 values are much lower than the 1979-2000 values.  This is often one of the most challenging conditions to explain to the public.  “Normal”, scientifically defined, is often different than “normal” as most people refer to it.  U.S. temperature anomalies reported in the past couple of years refer to a similar 1981-2010 “normal period”.  Those anomalies are smaller in value than if they were compared to the previous 1971-2000 “normal period”.  Thus, temperature anomalies don’t seem to increase as much as they would if scientists referred to the same reference period.

Arctic Sea Ice

According to the NSIDC, sea ice melt during June measured 2.10 million sq. km.  This melt rate was slower than normal for the month, but June′s extent remained below average – a condition the ice hasn’t hurdled since this time last year.  Instead of measuring near 11.89 million sq. km., June 2013′s average extent was only 11.5 million sq. km., a 300,000 sq. km. difference.

Barents Sea (Atlantic side) ice remained below its climatological normal value during the month, which continues the trend that began this last winter.  Kara Sea (Atlantic side) ice temporarily recovered from its wintertime low extent and reached normal conditions earlier this year, but fell back below normal during May through June.  Arctic Basin sea ice (surrounding the North Pole) fell below normal during June due to earlier weather conditions that sheared ice apart.  The Bering Sea (Pacific side), which saw ice extent growth due to anomalous northerly winds in 2011-2012, saw similar conditions in December 2012 through March 2013.  Since then, Bering Sea ice extent returned to normal for this time of year: zero.  The previous negative Arctic Oscillation phase gave way to normal conditions throughout June.  However, a stronger than normal Arctic Low set up which kept Arctic weather conditions cooler and stormier than normal.  These conditions prevented Arctic sea ice from melting as quickly in June as it did in 2012.  In the past few days, these conditions eased and rapid Arctic melt is once again underway.  I’ll have more to say about this in next month’s post.

For the first time in a number of years, Arctic sea ice extent in June didn’t reach a bottom-ten status.  June Arctic sea ice extent was “only” the 11th lowest on record.  In terms of climatological trends, Arctic sea ice extent in June decreased by 3.6% per decade.  This rate is closest to zero in the late winter/early spring months and furthest from zero in late summer/early fall months.  Note that this rate also uses 1981-2010 as the climatological normal.  There is no reason to expect this rate to change significantly (much more or less negative) any time soon, but negative rates are likely to slowly become more negative for the foreseeable future.  Additional low ice seasons will continue.  Some years will see less decline than other years (e.g., 2011) – but the multi-decadal trend is clear: negative.  The specific value for any given month during any given year is, of course, influenced by local and temporary weather conditions.  But it has become clearer every year that humans have established a new climatological normal in the Arctic with respect to sea ice.  This new normal will continue to have far-reaching implications on the weather in the mid-latitudes, where most people live.

Arctic Pictures and Graphs

The following graphic is a satellite representation of Arctic ice as of June 13, 2013:

Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20130613.

The following graphic is a satellite representation of Arctic ice as of July 4, 2013:

Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20130704.

Continued melt around the Arctic ice periphery is evident in the newest figure.  Hudson Bay ice is nearly gone.  Rapid melt is also evident in the Kara, Barents, and Bering Seas.  Compared to last year at the same time, more ice is present in the Baffin/Newfoundland, Beaufort, and Kara Seas.  This is due to interannual weather and sea variability.  The climate trend remains clear: widespread and rapid sea ice melt is the new normal for the Arctic.

So far, the early season thinning of sea ice near the North Pole hasn’t caused a mid-season mid-ocean collapse of sea ice, as many people feared.  This is not to say that rapid ice melt in the central Arctic Ocean will not happen this year.  We simply have to wait and see what happens before we issue obituaries.

The following graph of Arctic ice volume from the end of June demonstrates the relative decline in ice health with time:

Figure 3 – PIOMAS Arctic sea ice volume time series through June 2013.

As the graph shows, volume (length*width*height) hit another record minimum in June 2013.  Moreover, that volume remained far from normal for the past three years in a clear break from pre-2010 conditions.  Conditions between -1 and -2 standard deviations are somewhat rare and conditions outside the -2 standard deviation threshold (see the line below the shaded area on the graph above) are incredibly rare: the chances of 3 of them occurring in 3 subsequent years under normal conditions are extraordinarily low (you have a better chance of winning the Powerball than this).  Hence my assessment that “normal” conditions in the Arctic shifted from what they were in the past few centuries; humans are creating a new normal for the Arctic.  Note further that the ice volume anomaly returned to near the -1 standard deviation envelope in early 2011, early 2012, and now early 2013.  In each of the previous two years, volume fell rapidly outside of the -2 standard deviation area with the return of summer.  That provides further evidence that natural conditions are not the likely cause; rather, the more likely cause is human influence.

Arctic Sea Ice Extent

Take a look at May’s areal extent time series data:

Figure 4 – NSIDC Arctic sea ice extent time series through early July 2013 compared with five recent years’ data, climatological norm (dark gray line) and standard deviation envelope (light gray).

As you can see, this year’s extent (light blue curve)  remained at historically low levels throughout the spring, well below average values (thick gray curve), just as it did in the previous five springs.  Sea ice extent did something different this spring and early summer: the late season surge of ice formation seen in the  2009, 2010, and 2012 curves was not as strong this year; the early summer surge of ice melt seen in the 2010, 2011, and 2012 curves was also not as strong this year, at least not until the last week or so.  This graph also demonstrates that late-season ice formation surges have little effect on ice extent minima recorded in September each year.  The primary reason for this is the lack of ice depth due to previous year ice melt.  I will pay close attention to this time series throughout June to see if this year’s curve follows 2012′s.  Note the sharp decrease in sea ice extent in mid-June 2012.  That helped pave the way for last year’s record low September extent, even though weather conditions were not as a factor as they were during the 2007 record low season.

Figure 5 – Graph comparing two climatological normal periods: 1979-2000 (light blue solid line with dark gray shaded envelope) and 1981-2010 (purple solid line with light gray shaded envelope).  Also displayed is the Arctic sea ice extent for 2012 (green dashed line) and 2013 (light purple solid line).

This figure demonstrates the effect of adding ten years’ of low sea ice extent data in a data set’s mean and standard deviation values.  The 1981-2010 mean is lower than the 1979-2000 mean for all dates but the difference is greatest near the annual minimum extent in mid-September.  Likewise, the new standard deviation is much larger than the previous standard deviation.  This means that recent variance exceeds variance from the previous period.  This shows graphically what I’ve written about in these posts: the Arctic entered a new normal within the past 10 years.  What awaits us in the future?  For starters, scientists expect that the annual minimum extent will nearly reach zero.  The timing of that condition remains up for debate.  I think it will happen within the next ten years, rather than thirty years as others predict.

Antarctic Pictures and Graphs

Here is a satellite representation of Antarctic sea ice conditions from June 13, 2013:

Figure 6 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20130613.

And here is the corresponding graphic from July 4, 2013:

Figure 7 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20130704.

Sea ice growth in the past two months is within climatological norms.  However, there is more Antarctic sea ice today than there normally is on this calendar date.  The reason for this is the presence of early-season extra ice in the Weddell Sea (east of the Antarctic Peninsula that juts up toward South America).  This ice existed this past austral (Southern Hemisphere) summer due to an anomalous atmospheric circulation pattern: persistent high pressure west of the Weddell Sea.  This pressure system caused winds that pushed the sea ice north and also moved cold Antarctic air over the Sea, which kept ice melt rate well below normal.  A similar mechanism helped sea ice form in the Bering Sea last winter.  Where did the anomalous winds come from?  We can again point to a climatic relationship.

The difference between the noticeable and significant long-term Arctic ice loss and relative lack of Antarctic ice loss is largely and somewhat confusingly due to the ozone depletion that took place over the southern continent in the 20th century.  This depletion has caused a colder southern polar stratosphere than it otherwise would be.  Why?  Because ozone heats the air around it after it absorbs UV radiation and re-radiates it to its environment.  Will less ozone, there is less stratospheric heating.  This process reinforced the polar vortex over the Antarctic Circle.  This is almost exactly the opposite dynamical condition than exists over the Arctic with the negative phase of the Arctic Oscillation.  The southern polar vortex has helped keep cold, stormy weather in place over Antarctica that might not otherwise would have occurred to the same extent and intensity. The vortex and associated anomalous high pressure centers kept ice and cold air over places such as the Weddell Sea this year.

As the “ozone hole” continues to recover during this century, the effects of global warming will become more clear in this region, especially if ocean warming continues to melt sea-based Antarctic ice from below (subs. req’d).  The strong Antarctic polar vortex will likely weaken back to a more normal state and anomalous high pressure centers that keep ice flowing into the ocean will not form as often.  For now, we should perhaps consider the lack of global warming signal due to lack of ozone as relatively fortunate.  In the next few decades, we will have more than enough to contend with from Greenland ice sheet melt.  Were we to face a melting West Antarctic Ice Sheet at the same time, we would have to allocate many more resources.  Of course, in a few decades, we’re likely to face just such a situation.

Finally, here is the Antarctic sea ice extent time series through early July:

Figure 8 – NSIDC Antarctic sea ice extent time series through early July 2013.

The 2013 time series continues to track near the top of the +2 standard deviation envelope and above the 2012 time series.  Unlike the Arctic, there is no clear trend toward higher or lower sea ice extent conditions in the Antarctic Ocean.

Policy

Given the lack of climate policy development at a national or international level to date, Arctic conditions will likely continue to deteriorate for the foreseeable future.  This is especially true when you consider that climate effects today are largely due to greenhouse gas concentrations from 30 years ago.  It takes a long time for the additional radiative forcing to make its way through the climate system.  The Arctic Ocean will soak up additional energy (heat) from the Sun due to lack of reflective sea ice each summer.  Additional energy in the climate system creates cascading and nonlinear effects throughout the system.  For instance, excess energy pushes the Arctic Oscillation to a more negative phase, which allows anomalously cold air to pour south over Northern Hemisphere land masses while warm air moves over the Arctic during the winter.  This in turn impacts weather patterns throughout the year across the mid-latitudes and prevents rapid ice growth where we want it.

More worrisome for the long-term is the heat that impacts land-based ice.  As glaciers and ice sheets melt, sea-level rise occurs.  Beyond the increasing rate of sea-level rise due to thermal expansion (excess energy, see above), storms have more water to push onshore as they move along coastlines.  We can continue to react to these developments as we’ve mostly done so far and allocate billions of dollars in relief funds because of all the human infrastructure lining our coasts.  Or we can be proactive, minimize future global effects, and reduce societal costs.  The choice remains ours.

Errata

Here are my State of Polar Sea Ice posts from June and May 2013. For further comparison, here is my State of Polar Sea Ice post from July 2012.